What to look for in a TM.......

    I could not wait, so went into my files to post an article that I wrote 5 years ago on TM performance. I hope some of you enjoy it.............

Posted By Kenneth Harris on 6/9/2001 at 2:59 PM
Some people will always be impressed by "Big" numbers put out by some manufacturers, but here are the facts.

A truckmount only has to do 3 things to work well:

1. Pressurize water to 600 psi or so.
2. Heat the water to 200-250 degrees F.
3. Be capable of generating about 300 cfm with 14" HG lift.

Now lets examine these points one by one to see what it takes to meet these numbers and why you don't need more than this.

1. This is the easy one. It takes less than 1 HP to generate 600 psi in pressure from your pump.Why you need this much is to acheive good flushing of the soil in the carpet once emulsifing has taken place. This much pressure will give you around 2 gpm with a .06 jet or combination thereof. More than this pressure and you may overwet the carpet backing.All truckmounts can make this pressure; 14 hp and up.


2.The reason you want your system to be capable of heating your water to 200 to 250 degrees ATW is to get the highest cleaning power from your emulsifier( if you use one).The closer you can get it to 212 degrees f (at sea level), the better it works.Drying times of the carpet get less too. The reason you want 250 degrees F if you can get it, is because the water when it leaves the jet(s) on your wand will cool down about 50 degrees while travelling the 2"-3" to the carpet.Nearly all kerosene and some propane systems(250,000 btu) will get you these temperatures.These will often be used with a 20-25 hp machine. If a heat exchanger is used to heat the water, a larger hp engine(25-30 hp) will need to be used to generate a higher BTU output. Going higher than this will generate more heat, at the cost of more weight,gas usage, and expense. But since 250 can be acheived with much less than this, its not necessary.

3.This is the area where most people get confused with a lot of " Big" numbers being thrown around. While it may impress some of your friends when you tell them that your truckmount puts out 400 cfm when you clean carpets,it isn't so.This number only exists on a 4.7 roots blower when turned at 3000 rpm, with no plumbing, tank, hoses or wand attached to it!In the real world we all have to have wands and hoses attached to our machines.Since nearly 100% of us use 2" hose, we can't move more than 310 cfm here.And since over 90% of us use at least a 10 ft 1.5" whip hose at the end of that, the airflow goes down to at least 225 cfm.Now, when we add on our 1.5"tubed-12" wide cleaning wand; airflow drops to about 150 cfm at 14"HG at the interface with the carpet!Isn't exactly 400 cfm anymore. And how much HP does it take to use a 4.7 roots blower for this senario? Only 15hp!For most people a 4M blower( 320cfm-12hp) is all they need given the airflow restrictions of the hoses and wand.But even if you only had a 3.6 for a blower (280 cfm-9hp overdriven), you still wouldn't notice much difference at the wand! The most power you need to drive any of these blowers is 25HP( allowing some reserve for power drop-off as the engine ages).More than this goes out the exhaust as burned fuel.More than this increases the resistance of the air flow in the rest of the system and makes your vacuum relief valve open more often. If you dual wand( and 90% don't) then you have a need for 400+ cfm. For the rest of us its simply NOT needed!

Ken Harris